<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="https://code.jquery.com/jquery-1.12.4.js"></script>
</head>

<body>
    <div id="big">
        <input type="checkbox" value="1" name="check" checked="checked" />
        <input type="checkbox" value="2" name="check" />
        <input type="checkbox" value="3" name="check" checked="checked" />
        <input type="checkbox" value="4" name="check" />
    </div>

    <table id="tab">
        <tbody>
            <tr>
                <td>第一行</td>
                <td>第一行</td>
            </tr>
            <tr>
                <td>第二行</td>
                <td>第二行</td>
            </tr>
            <tr>
                <td>第三行</td>
                <td>第三行</td>
            </tr>
            <tr>
                <td>第四行</td>
                <td>第四行</td>
            </tr>
            <tr>
                <td>第五行</td>
                <td>第五行</td>
            </tr>
        </tbody>
    </table>
</body>
<script type="text/javascript">
    var div = $('#big')[0];
    var input = $('input');

    div.onchange = () => {
        var a = $('input:checked');
        console.log(a.length);
    }

    var tr = $('tr');
    var len= tr.length;
    console.log(tr);
    for (let index = 1; index < len-1; index++) {
        if (index%2!=0) {
            tr[index].style.color='red';
        }
    }
</script>

</html>